In a device of an image forming apparatus such as a printer, an electrophotographic copying machine, or a facsimile machine which is believed to require semi-conductivity, a conductive member such as a conductive roll, a conductive blade, or a conductive belt is used.
Depending on specific use, various properties including conductivity within a desired range (electrical resistance value and its variation, dependence on environment, and dependence on voltage), non-contaminating property, low hardness, and dimension stability are required for the conductive member.
As a way of providing conductivity to rubber for constituting part of a conductive member, a method of adding a small amount of a conductivity imparting material such as carbon black or metal oxide to rubber and dispersing it therein to control the electrical resistance of a conductive member is known. However, according to this method, it is difficult to control the dispersity of a small amount of the conductivity imparting material added by kneading and, since the dispersion state of the conductivity imparting material is changed according to flow of rubber during molding and cross-linking, causing a variation in electrical resistance value, and therefore there is a problem that a sharp image is difficult to be obtained.
Therefore, as a solution for the variation in electrical resistance value, polyether rubber or the like having semi-conductivity by itself without being added with a conductivity imparting material has been used as a conductive member. However, in recent days, high speed is required for an image forming apparatus, and the conductive member, in particular a conductive roll, requires to have even lower electrical resistance. As a method of lowering electrical resistance, increasing the unit amount of an ethylene oxide monomer as one of the constituent units of polyether rubber is effective. However, when the unit amount of an ethylene oxide monomer is increased, the rubber itself becomes water soluble, and therefore it may be difficult to produce it. Further, there is also a problem that it causes contamination of a photoconductor. Therefore, according to conventional methods, the unit amount of an ethylene oxide monomer in polyether rubber can be increased only to a certain level, and as a result, requirements for having low electrical resistance may not be fully satisfied.
Further, there has been conventionally a problem that, under application of voltage to a conductive member, upon continuous use, the conductive member deteriorated due to electric current so that electrical resistance value of the conductive member increases and quality of an image is impaired accordingly. For solving this problem, for example, Patent Document 1 discloses polyether rubber which contains 0.1 mol % to less than 30 mol % of units of monomer which has onium ion introduced by using an aliphatic amine such as n-butyldimethylamine, and trimethylamine, as an onium-forming agent. However, the cross-linked rubber which is obtained by using the polyether rubber which is described in this Patent Document 1 has little variation in electrical resistance value, has low electrical resistance value, and is suppressed in increase in electrical resistance value even in the case of continuous use, but is insufficient in compression set resistance. For this reason, improvement of compression set resistance has been desired.